...not only are there limestone caves that are a Muslim pilgrimage site, but check out all the cool geologic images on this page:
The blogger writes about the cave: "An iron ladder, about five meters high, led to the small entrance of the cave. An overweight person could not enter it. Noé and I followed the group and they soon were engulfed into the rock. The tradition wants it that if someone cannot pass the narrow entrance of the cave, he/she is not the child of his/her father."
The cave is purported to be connected to Adam and Eve, Hazrat Ali, and Noah's Ark (http://www.pakistanpressfoundation.org/arts-and-culture/54842)
Image credit: http://www.panoramio.com/user/1092747/tags/Lahut LaMakan